System and Method for Synchronization and Link Acquisition in Cellular Wireless Systems with Directional Antennas

ABSTRACT

A system and a method for synchronization and link acquisition in cellular wireless systems with directional antennas are disclosed. In an embodiment a method for wireless communication includes synchronizing, by a first network controller, transmission of a first synchronization signal with transmission of a second synchronization signal from another network controller.

TECHNICAL FIELD

The present disclosure relates to a system and method for wirelesscommunications, and, in particular embodiments, to a system and methodfor synchronization and link acquisition in cellular wireless systemswith directional antennas.

BACKGROUND

In order to connect to a wireless cellular system such as high-speedpacket access (HSPA) and long-term evolution (LTE), the user equipment(UE) conventionally searches for signals transmitted by network(infrastructure) entities such as base stations (BSs) ortransmitter-receiver points (TRPs). The term TRP is used herein to referto any network component or network controller such as a base station oraccess point.

The first signals acquired and detected by the UE are calledsynchronization (sync) signals whose role is to communicate importantinformation to the UE, e.g., a cell identifier (ID), symbol and frametiming information, etc. A sync signal in this disclosure may refer to aset of one or more signals that communicate such information and may ormay not occupy consecutive time and/or frequency resources. An exampleis the long-term evolution (LTE) system where a sync signal is composedof a primary sync signal (PSS) and a secondary sync signal (SSS), whichmay or may not occupy successive symbol times depending on the systemconfiguration. Once a UE obtains such information by detecting a syncsignal from a TRP, it can initiate a connection procedure to the TRP.

Due to mobility and other phenomena impacting the channel quality, a UEmay need to connect to, or benefit from connecting to, another TRP whilestaying connected to the same network. This procedure is calledhandover. For this purpose, a UE maintains a list of potential handoverdestinations and their channel quality by continuously listening to thewireless medium and detecting sync signals from nearby TRPs. Thisinformation can be reported to the network through the TRP currentlyserving a UE. The network or the UE can then decide whether and when ahandover is necessary or beneficial.

SUMMARY

An embodiment of the disclosure provides a method for wirelesscommunication, wherein the method includes synchronizing, by a firsttransmitter-receiver point (TRP), and transmission of a first syncsignal with transmission of a second sync signal by another TRP.

Another embodiment of the disclosure provides a method for wirelesscommunication, wherein the method includes transmitting, by a networkcontroller, reference signals (RS) for beam management to a userequipment (UE), receiving, by the network controller, a plurality ofreported beams from the UE and signaling, by the network controller,scheduling instructions to the UE based on the received beams so thatthe UE is configured to search for synchronization signals with at leastone first beam using a first antenna set while still being able toreceive bearer data with at least one second beam using a second antennaset during a first time period for synchronization, wherein the firstantenna set and the second antenna set are non-overlapping.

Yet another embodiment of the disclosure provides a method for wirelesscommunication, wherein the method includes receiving, by a userequipment (UE), reference signals (RS) for beam management from anetwork controller, reporting, by the UE, a plurality of beams to thenetwork controller and receiving, by the UE, scheduling instructionsfrom the network controller based on the sent beams so that the UE isconfigured to search for synchronization signals with at least one firstbeam using a first antenna set while still being able to receive bearerdata with at least one second beam and using a second antenna set duringa first time period for synchronization, wherein the first antenna setand the second antenna set are non-overlapping.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIGS. 1A and 1B illustrate sync signal acquisition failure when aconnected UE is employing analog beamforming;

FIG. 2 illustrates an example timeline corresponding to communicationsof FIG. 1;

FIGS. 3A and 3B illustrate an embodiment of the disclosure where TRP1and TRP2 communicate with UE1 and UE2;

FIG. 4 illustrates an example timeline corresponding to communicationsof FIGS. 3 (3A and 3B) according to an embodiment;

FIG. 5 illustrates an example of a reduced-layer communication interval(RLCI) according to an embodiment;

FIG. 6 illustrates an example of RLCI scheduling according toembodiments;

FIGS. 7A and 7B illustrate a beam (B1) applied by an antenna inreduced-layer communications being identical to the beam (B1) applied bythat antenna for full-layer communication according to an embodiment;

FIGS. 8A and 8B illustrate a beam (B3) applied by an antenna inreduced-layer communications being different from the beam (B1) appliedby that antenna for full-layer communication according to an embodiment;

FIGS. 9-11 illustrate a block diagram of an embodiment processing systemfor performing methods described herein according to embodiments;

FIG. 12 illustrates a block diagram of a transceiver adapted to transmitand receive signaling over a telecommunications network according to anembodiment;

FIG. 13 illustrates a block diagram of an embodiment processing systemfor performing methods described herein; and

FIG. 14 illustrates a block diagram of a transceiver adapted to transmitand receive signaling over a telecommunications network.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The structure, manufacture and use of the presently preferredembodiments are discussed in detail below. It should be appreciated,however, that the present disclosure provides many applicable inventiveconcepts that can be embodied in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use the disclosure, and do not limit the scope of thedisclosure.

When antenna(s) of a user equipment (UE) are able to listen to alldirections to receive synchronization (sync) signals from nearbytransmission points (TRPs), the sync signal detector in the UE candetect sync signals even in the presence of interfering signalsproviding that the signal quality is sufficiently high and theinterference is not too severe. However, if antenna(s) of a UE areunable to listen to all directions at a time, there is a nonzeroprobability that the UE misses to detect sync signals from a nearby TRP.An example of this situation is when a UE uses directional antennas or,equivalently, adopts beamforming at its antenna(s) when listening to thewireless medium. In this scenario, since the UE is directing its“listening beam” towards its serving TRP, it may not be able to receivesync signals from nearby TRPs, hence missing a chance to performhandover when a TRP with better channel quality is available.

This problem is particularly important in the case of millimeter-wave(mmWave) access systems where the use of directional antennas and analogbeamforming is practically inevitable due to lower link budget comparedto legacy microwave systems operating at lower frequencies, e.g., lowerthan 6 GHz.

The issue is illustrated in FIGS. 1A and 1B, in which each TRP 10, 20transmits multiple sync signals and/or multiple copies of a sync signal11, 21 in multiple directions either by using one antenna sequentiallyor by using multiple antennas simultaneously or a combination thereof.FIGS. 1A and 1B illustrate sync signal acquisition failure when aconnected UE 15, 25 is employing analog beamforming. In FIG. 1A, UE1 15is receiving data from (its serving) TRP1 10 and is unable to receivesync signals 21 from the nearby TRP2 20. Subsequently, in FIG. 1B, whenUE1 15 searches for sync signals 21 from nearby TRPs, TRP2 20 is nottransmitting sync signals 21.

FIG. 2 illustrates an example of a timeline corresponding tocommunications in FIGS. 1(A and B). Different shading patterns in syncsignal transmission correspond to multiple sync signals and/or multiplecopies of a sync signal transmitted to different directions. As can beseen from FIG. 2, TRP1 10 and TRP2 20 send sync signals at differenttimes and their respectively connected UEs, UE1 15 and UE2 25, searchfor the sync signal at different times.

Various embodiments of the disclosure provide transmission of syncsignals from various TRPs wherein the TRPs coordinate the transmissionof the sync signals. For example, the sync signals from the various TRPsmay be transmitted during a time interval such as asynchronization-signal-dedicated interval (SSDI). The SSDI may betransmitted between two time intervals in which each TRP communicateswith their connected UEs by transmitting bearer data and control data(other than sync signals). Transmitting sync signals during a definedSSDI is advantageous because the UE is able or has a near 100% certaintyto detect the sync signal(s) with its directional antenna.

Various other embodiments of the disclosure provide a higherlayer/antenna communication between a TRP and a UE during acommunication period and a lower layer/antenna communication during areduced-layer communication interval (RLCI). During the RLCI the UE mayuse the freed up layer(s)/antenna(s) for searching for sync signals ofother TRP(s). After the RLCI, the UE may switch back to a higherlayer/antenna communication. The TRP and the UE may communicate via afirst and a second beam pair during a high layer/antenna communicationand via a first beam pair during the RLCI. Alternatively, the TRP and UEmay communicate via a first and a second beam pair during a highlayer/antenna communication and via a third beam pair during the RLCI,wherein third beam pair is different than the first and second beampairs. Having the UE receiving sync signals during t RLCI with a firstantenna/layer set while at the same time receiving data with a secondantenna/layer set is advantageous since such a method is very efficientand provides uninterrupted data transmission.

FIGS. 3A and 3B show an embodiment of the present disclosure. MultipleTRPs (TRP1 30 and TRP2 40) in a vicinity of a UE1 30 synchronize theirsync signal transmissions or limit those transmissions to specific timeperiods (e.g., intervals). The TRPs 30, 40 synchronize their sync signaltransmission over the backhaul 36 (e.g., X2 interface). The TRPs maysend the sync signals only at a synchronization-signal-dedicatedinterval (SSDI) between two communication time periods. These intervalsmay be configured over the backhaul 36. During SSDIs, the UE1 35 canchange its antenna beam(s) 31, 32 and search for sync signals 33, 43from some or all other directions. These directions may be differentthan the direction covered by the serving TRP1 30. If a TRP 30, 40 hasthe capability to use multiple beams through any of its antennas, it maychoose to switch from one beam to another beam during an SSDI fortransmitting multiple sync signals or multiple copies of a sync signal33, 43. A UE 35, 45 may also choose to switch beams through itsantenna(s) during an SSDI in order to increase the number of directionsit listens to. The order of beams by the TRP 30, 40 and/or the UE 35, 45may be known a priori or may be decided by the TRP 30, 40 and/or the UE35, 45 at each point.

FIG. 3A illustrates TRP1 30 and TRP2 40 communicating (by sending bearerdata or control data) with UE1 35 and UE2 45, respectively. FIG. 3Billustrates TRP1 30 and TRP2 40 transmit sync signals 33, 43 during anSSDI. UE1 35 connected to its serving TRP1 30 can successfully detectsync signals 43 from TRP2 40 during an SSDI.

FIG. 4 illustrates an example of a timeline corresponding tocommunications in FIG. 3. Different shading patterns in sync signaltransmission can correspond to multiple beams (sync signals and/ormultiple copies of a sync signal) transmitted to different directions.In particular, FIG. 4 shows TRP1 and TRP2 sending three different syncsignals (in three different beams) while UE1 only searches with onebeam. However, in various other embodiments, UE1 can search withdifferent beams and the TRPs can send sync signals in just one or aplurality of different beams.

Reduced-Layer Communication Interval

FIG. 5 shows yet another embodiment of the present disclosure. A servingTRP 50 may use certain time periods for the UE 55 to search for syncsignals from other TRPs. During these periods, the TRP 50 either (1)does not allocate resources for communication (bearer data or controldata) with the UE 55, or (2) reduces the number of antennas (representedby associated beams, e.g., from 2 beams 56, 57 to one beam 58) requiredby the UE 55 for receiving data if the UE 55 has multiple antennas.Therefore, during these time periods, the UE 55 will have one ormultiple antennas (and associated beam(s) 59) that are not busycommunicating with the serving TRP 50 and will be available fordetecting sync signals from one or multiple directions other than thedirection covered by the serving TRP 50.

As an example, consider a multiple-input multiple-output (MIMO)multiplexing system where a TRP with M transmit antennas transmits Lstreams of data, also known as “layers” of data, to a UE with Nantennas. This system is called an M×N MIMO multiplexing system wherethe number of data layers L cannot exceed the minimum of M and N, i.e.,L<min{M,N}. Therefore, in order for the UE 55 to be able to use asmaller number of antennas, the number of data layers may have to bereduced. A time period (e.g., interval) that a UE communicates with areduced number of data layers is called a reduced-layer communicationinterval (RLCI) hereafter. Communication between a TRP 50 and a UE 55 iscalled reduced-layer communication during an RLCI and is calledfull-layer communication otherwise (or a full-layer communicationinterval (FLCI)).

For example, consider a 2×2 MIMO multiplexing system, e.g., a TRP 50 anda UE 55 each with 2 antennas (producing the beams 51-53 for the TRP 50and beams 56-59 for the UE 55). When the UE 55 uses both of its antennas(represented by beams 56, 57), the TRP 50 can transmit 2 data layers tothe UE 55. However, if the UE 55 uses only one antenna (represented bybeam 58), the TRP 50 cannot transmit more than 1 data layer to the UE55. Therefore, the TRP 50 can schedule 2-layer communication for regularcommunication with the UE 55, but switch to 1-layer communication duringRLCIs.

Similarly, the MIMO multiplexing system can be a 4×4 or an 8×8 MIMOmultiplexing system. Accordingly, for a 4×4 MIMO, the TRP 50 canschedule 4-layer, 3-layer or 2-layer communication for regularcommunications with the UE 55, but switch to 3-layer, 2-layer or 1-layercommunication during RLCIs.

It should be noted that reduced-layer communication is a special case ofa reduced antenna communication. Reduced-layer communication andfull-layer communication can be generalized as reduced-antennacommunication and full-antenna communication. In other words,reduced-antenna communication and full-antenna communication mean acommunication with a subset of antennas and a communication with all ofthe antennas, respectively. An example of reducing the number ofantennas without reducing the number of layers is MIMO diversity schemeswhere multiple antennas are used to provide a high quality signal forone data layer. In such schemes, decreasing the number of antennas forone data layer reduces the average signal quality for that data layerwhile increasing the number of antennas for that data layer increasesthe average signal quality for that data layer. As will be discussed indetails later in this document, reducing the number of antennas withoutreducing the number of layers may still demand separate beamforming andCSI acquisition processes, each corresponding to a certain number ofantennas.

If the TRP configures the RLCIs periodically or semi-persistently, theUE can switch to a lower rank automatically without requiring the TRP toschedule a lower-rank communication for each RLCI.

A special case of an RLCI is a 0-layer RLCI, which is essentially a timegap when a UE can use all its antennas for detection of sync signalsfrom other directions. For example, in order to schedule an RLCI for aUE with only 1 antenna, a TRP needs to schedule time gaps for which nocommunication is scheduled with the UE.

When a TRP has a larger number of antennas, the TRP can communicate withmore than one UE simultaneously. This scheme is called multiuser-MIMO(MU-MIMO). An example of MU-MIMO during an RLCI is as follows: considera system of one TRP having 2 antennas and two UEs, each with 2 antennas.The TRP can schedule 2×2 MIMO multiplexing communication with each UE.If, for example, all the bandwidth is allocated to one UE at a time,communication between the TRP and each UE is scheduled at a separatetime period. However, the TRP may choose to schedule an RLCI for MU-MIMOwith both of the UEs simultaneously. During the RLCI, the TRP schedulestwo 1-layer communication, each layer with one of the UEs. Sincecommunication with each of the UEs needs only one UE antenna, each UE isfree to use the other antenna for detection of sync signals from otherdirections.

RLCI scheduling is the process of determining and signaling an RLCIduration, an inter-RLCI period, a number of layers for reduced-layercommunication during an RLCI, and other RLCI parameters between a TRPand a UE. RLCIs may be scheduled and signaled by the TRP, but othervariations are not precluded.

FIG. 6 shows several embodiments of an RLCI scheduling:

In one embodiment, a TRP schedules the RLCIs for a UE persistently orsemi-persistently at fixed inter-RLCI periods. The duration of each RLCIand the inter-RLCI periods can be signaled to the UE explicitly orimplicitly through, for example, gaps in communications scheduled withthat UE. Duration of an RLCI can be chosen in a way that reduces theprobability that a UE misses to detect a sync signal transmission by anearby TRP. For example, if nearby TRPs transmit sync signals in periodsof less than or equal to T, and if the duration of transmitting a syncsignal is τ, then the TRP may choose to schedule an RLCI with a minimumduration of T+τ.

As can be seen from FIG. 6, UE is served by TRP1. During RLCI, UE canuse some or all of its antennas (layers) to detect sync signals fromother TRPs, e.g., TRP2 and TRP3.

In further embodiments, if the values of T and τ are different from oneTRP to another TRP in a vicinity of the UE, a minimum RLCI durationequal to the maximum of T+τ over various TRPs can be considered as asafe bet.

In yet further embodiments, if a TRP transmits sync signal(s) to one ormore certain directions during the period τ and it takes a period of n×Tto cover all the directions, a minimum RLCI duration of n×T+τ can beconsidered as a safe bet.

In various embodiments, if the RLCI duration is shorter than the minimumRLCI duration determined by the aforementioned embodiments, inter-RLCIperiods may be chosen variably. Such a procedure may increase theprobability of a UE detecting a sync signal from a nearby TRPsuccessfully. For example, if sync signals are transmitted by a nearbyTRP at periods of T and the RLCI duration τ is only T/2, if RLCIs arescheduled at periods of every n×T where n is an integer, a UE may missall sync signal transmissions by the nearby TRP. In this example,inter-RLCI periods may be chosen variably to increase the probability ofthe UE detecting a sync signal from the nearby TRP. This method can beimplemented by the TRP and/or triggered by the UE itself.

In the aforementioned embodiments, information about sync signaltransmissions by nearby TRPs such as the duration of the transmissions(τ) and the period between the transmissions (T) may be eitherpredetermined or obtained through the network (backhaul) or obtainedthrough UE reports or other methods.

Triggering RLCI Scheduling

In the following, several embodiments for triggering RLCI scheduling areprovided.

In one embodiment, RLCI scheduling may be periodic determined by presetsystem parameters. A simple example is when all TRPs in a vicinity havesimilar preset values for sync signal transmission duration (τ) and theperiod between sync signal transmissions (T). In this case, the TRP cansignal periodic RLCIs persistently or semi-persistently to a UE.

In another embodiment, RLCI scheduling may be aperiodic triggered by aTRP as a function of various system parameters such as traffic, possiblyvariable parameters of sync signal transmission by nearby TRPs, signalquality between the TRP and a UE that makes a handover more likely, orother factors.

In yet another embodiment, RLCI scheduling may be aperiodic triggered bya UE as a function of signal quality between the UE and its serving TRPthat makes a handover more likely, or other factors.

In yet another embodiment, RLCI scheduling may be a combination of theaforementioned embodiments. For example, periodic RLCIs may be scheduledby a TRP, but additional aperiodic RLCIs may be triggered by the TRP ora UE.

Feedback for Reduced-Layer Communication

A MIMO multiplexing system normally requires channel state information(CSI) between antennas of a transmitter and antennas of a receiver. Thisinformation may include channel quality indicators (CQIs), precodingmatrix indicators (PMIs), rank indicators (RIs), or other information.Depending on the multiplexing scheme, this information is normallyprovided for the transmitter and possibly provided for the receiver.When the transmitter and/or the receiver use directional antennas thatemploy, for example, analog beamforming, the quality of the channel forMIMO multiplexing usually depends on the beams adopted by each antenna.One of the factors that may determine which beams provide a higherchannel quality is the number of multiplexed data layers. Therefore, inorder to realize efficient reduced-layer communication, CSI for asmaller number of layers may be required or be beneficial in addition toCSI for full-layer communication.

A TRP 60 and a UE 70 reduce the number of communication layers by simplyusing a subset of antennas used for full-layer communication. FIGS. 7 (Aand B) and 8 (A and B) show a TRP 60 with antennas employing beamformingfor a plurality of beams (e.g., beams 61, 62, 63, wherein beam 63 can beeither beam 61 or beam 62, or different from bean 61 and beam 62) andthe UE 70 having antennas employing beamforming for a plurality of beams(e.g., two beams B1, B2). Of course, the TRP 60 and the UE 70 can havemore than two antennas and therefore provide more than two beams (e.g.,four beams or eight beams). Data (e.g., bearer data) can be transmittedbetween the TRP 60 and the UE 70 via the beams 61, 62, B1, B2.

In an embodiment, for FIG. 7 (A and B), when in reduced-layercommunication a beam B1 from the plurality of beams B1, B2 provided bythe UE antenna can be chosen identical to the beam B1 applied by thatantenna for full-layer communication. Accordingly, the beam B1 generatedby an antenna of the UE 70 in reduced-layer communication is identicalto the beam B1 generated by that antenna of the UE 70 for full-layercommunication. The subset of antennas selected for reduced-layercommunication can be selected by the TRP 60 or the UE 70 or it can benegotiated through signaling.

In another embodiment, the TRP 60 and the UE 70 perform separate channelmeasurements and/or separate (analog) beamforming training forfull-layer and reduced-layer communication. If the UE 70 needs to reportthe CSI to the TRP 60, or vice versa, separate reports can be sent forfull-layer and reduced-layer communication. FIGS. 8A and 8B illustratethat the UE 70 can switch from beams B1, B2 in full-layer communicationto a beam B3 generated by an antenna of the UE 70 in reduced-layercommunication. The beam B3 is different from the beam B1 or B2 generatedby that antenna for full-layer communication. The subset of antennasselected for reduced-layer communication can be selected by the TRP 60or the UE 70 or it can be negotiated through signaling.

FIG. 9 shows a flowchart of method 100 according to an embodiment torealize the embodiment of FIG. 8B. In a first step, at 110, the TRP mayconfigure transmission of one or multiple sets of reference signals(RSs) for beam management and/or CSI acquisition for a connected UE or agroup of connected UEs. At 120, the TRP may also configure multiple beamstate reporting and/or CSI reporting, where each reporting correspondsto a different subset of antennas. The TRP then transmits RSs for beammanagement and/or CSI acquisition. This is shown in step 130. At step140, each UE measures the RSs and, at step 145, each UE reports a set ofbeams and/or CSIs (i.e., rank indicator (RI), precoding matrix indicator(PMI), channel quality indicator (CQI), and/or so forth) back to theTRP, each corresponding to a different subset of antennas. At 150, theTRP may signal which set of beams and/or CSIs is adopted for eachscheduled communication. The TRP may, alternatively, signal which set ofbeams and/or CSIs is adopted for a scheduled communication only whendeviating from a default set of beams and/or CSIs. In yet anotherembodiment, signaling for a set of beams and/or CSIs may be implicit. Anexample of this alternative is an RLCI where a UE is implicitly informedthat the set of beams and/or CSIs adopted for communication during theinterval is different from the default, e.g., different from thefull-antenna communication. Moreover, indication of a set of beams tothe UE and/or CSIs may be based on quasi-co-location (QCL) indicatedbetween certain antennas. For example, a UE may have acquired andreported beam information and/or CSI on a channel with a subset ofantennas, but may need to assume certain set of beams and/or digitalprecoding corresponding to another subset of antennas. If the twosubsets are indicated quasi-co-located (QCLed), then the set of beamsand/or digital precoding can be assumed. At 160 the TRP precodes signalsfor each scheduled communication for the indicated set of beams(according to the associated earlier reporting) from step 150, and, at170, the UE receives signals for each scheduled communication.

FIG. 10 shows flowchart of method 100′ according to an embodiment torealize the embodiment of FIG. 8B. In contrast to the method 100 of theembodiment of FIG. 9, at least one reporting may be associated with RLCIcommunication. For example, the TRP may indicate to the UE that areporting from the set of configured reporting is associated with RLCIsat 120′. Then, the UE infers that the set of Rx antennas it selects forthe RLCI related reporting and its corresponding measurements may allowthe UE to search for sync signals from neighboring cells. When an RLCIis scheduled for the UE, the UE uses the Rx antenna set corresponding tothe reporting in order to receive downlink signal from other TRP(s). TheTRP transmits RSs for beam management and/or CSI acquisition to the UEat 130′. The UE performs measurements on the RSs at 140′ and reportsmultiple sets of beams and/or CSIs to the TRP, each corresponding to aconfigured reporting at 145′. This is shown in the flowchart where theTRP indicates precoded signals to the UE for full layer communicationsand for RLCI communication at 160′, and the UE receives these signalsfor full-layer communication and for RLCI communication accordingly at170′.

Furthermore, UE capability information such as the number of antennas,analog beamforming capabilities, and so forth can be communicated to theTRP. As an example, a UE that does not perform analog beamforming on anyof its antennas may not need to be scheduled any RLCIs, while a UE withone or more antennas that can sweep over a larger number of beams needsmore or longer RLCIs scheduled for it. As another example, a UE maydedicate one or more antennas to search for sync signals and dedicatethe other antennas to communications with the TRP to which it connects.In this case, the UE may not need any RLCIs scheduled for it. In yetanother example, the UE capability can be an indication, for instance,through a single bit, whether or not the UE will require RLCIs. UEcapability information can be communicated to a TRP during theconnection phase or later after the connection is established. This isshown in the flowchart where the TRP precodes signals full-layercommunication and reduced-layer communication accordingly at 160′ andthe UE receives signals for full-layer communication and reduced-layercommunication accordingly at 170′.

FIG. 12 shows flowchart of a method 100″ according to an embodiment torealize the embodiment of FIG. 8B. In contrast to the methods 100 and100′ the above method 100″ is extended to the case that each beam and/orCSI reporting is associated with a communication class. Examples of acommunication classes are full-layer communication, reduced-layercommunication, communications with a subset of antennas in general,communications at a low rate, communications at a low power, and soforth. Communication classes can be defined in the standard and known tothe network and to the UE in advance. Alternatively, communicationclasses can be defined by the network based on parameters such as thenumber of antennas required for measurement and reporting, the number ofmultiplexed communication layers, minimum rate requirements, and soforth. Then, when a reporting is configured for a particular class, at120″, the UE performs measurements and reports beam information and/orCSI according to the class requirements. For example, a full-layercommunication class demands the UE to perform measurements through allits antennas while a reduced-layer communication class demands the UE toperform measurements through a subset of its antennas. This is shown inthe flowchart where the TRP precodes signals for each scheduledcommunication according to its communication class at 160″ and the UEreceives signals for each scheduled communication according to itscommunication class at 170″.

In the above embodiments, when a TRP receives the feedback from a UE, itcan then use the feedback to decide about multiple RLCI parametersincluding inter-RLCI period, RLCI duration, number of layers and theantennas selected for reduced-layer communication, etc. A preferredconsideration by the TRP could be to ensure that the number of antennasfor reduced-layer communication provides sufficient gain that stillallows a minimum channel quality and communication rate between the TPRand the UE.

FIG. 12 illustrates a flow chart 200 of a transmission (Tx) andreception (Rx) timeline according to an embodiment for embodiments ofFIGS. 9-11. One or multiple configuration messages 210 from the TRPinforms a UE of parameters for reference signals for beamformingtraining and/or CSI acquisition and the corresponding beam and/or CSIreporting requested from the UE. At 220, the TRP sends the referencesignals and, at 230, the UE performs measurements on the referencesignals and reports multiple sets of beams and/or CSIs as configured bythe TRP. Thereafter, at 240, the TRP schedules the communication withthe UE and, at 250, precodes each communication to the UE in accordancewith either of the reports from the UE. An index corresponding toprecoding for each communication should be indicated to the UE,implicitly or explicitly, by the TRP. If the index is indicatedexplicitly it is done during scheduling at 240. If it is done implicitlyit is done, for example, during communication at 250. A special case ofsuch a scenario is where an RLCI overlaps with a full-layercommunication. An example of this case is the example of FIG. 12 wherereporting 1, Tx precoding 1, and Rx antenna set 1 correspond tofull-layer communication while reporting 2, Tx precoding 2, and Rxantenna set 2 correspond to reduced-layer communication. Note that theword ‘reporting’ is a short version of beam information reporting and/ora CSI reporting.

Spreading Sync Signals

In embodiments, TRPs multiply sync signals by spreading sequences. Thespreading sequence(s) should be sufficiently long to boost thesignal-to-interference-plus-noise ratio (SINR) for reception fromdirections suppressed by the directional antenna(s) at the UE. A specialcase is simple repetition of the sync signals. The UE may be aware ofthe spreading sequence(s) and, for example, use matched filtering to“de-spread” the received signals. If more than one spreading sequence isused for this purpose in the system, different spreading sequences canbe used to communicate additional information such as TRP-specific orbeam-specific IDs.

Erasure-Tolerant Transmissions

In yet another embodiment, downlink (DL) transmissions by the TRP areerasure-tolerant, i.e., the UE is able to receive/decode DL data even ifit partially misses the DL signals. Therefore, the UE will be able tosearch for sync signals from other TRPs while DL transmissions areongoing. There are multiple ways to realize an erasure-tolerant DLtransmission.

(1) Additional redundancy: By adding redundancy, i.e., lowering the coderate, the UE can search for sync signals from other TRPs. A simpleexample is repetition coding where each symbol or group of symbols istransmitted multiple times, which allows the UE to search for incomingsync signals from other directions and attempt to receive other copiesof the missed symbol or group of symbols at an earlier or later time.

(2) Rate-less coding: If a TRP employs rate-less codes such as fountaincodes, the UE can listen to its serving TRP and attempt to decode thesignal after receiving each symbol or group of symbols. Once the UE isable to decode the signal, it can change its receive beam to search forsync signals from other directions. In this approach, the UE's abilityto search for sync signals depends on whether and when it succeeds indecoding the rate-less codes.

(3) Non-consecutive resource allocation: If the resources allocated to aDL transmission are not consecutive, the UE can search for sync signalsfrom other TRPs at the time instants that no resources are allocated toit.

(4) Spreading: DL signals can be spread by multiplying the signals by aspreading sequence. The spread signals, then, need to be de-spread atthe UE. If UE does not receive a part of the signals, it may still beable to recover the signal, possibly at a lower signal-to-noise ratio(SNR).

Any such method can be implemented by the TRP or triggered/requested bythe UE.

Exploration vs. exploitation: In the aforementioned embodiment, a UE canchoose to maintain a balance between “exploration,” i.e., searching forsync signals from other directions, and “exploitation,” i.e., using theestablished link with its serving TRP for communications, as it may takedifferent performance and complexity criteria into account. For example,on the one hand, excessive exploration provides a better link qualitythat may be underutilized; on the other hand, excessive exploitationincreases the period of utilizing a link for communications, but thelink may not provide the highest channel quality available.

TRP-Aware Cell Search

In yet another embodiment, a TRP can schedule resources for each UE itis serving so that each UE will be able to perform sync signalacquisition from other directions in a timely manner. To this end, theTRP ensures that: each UE is allowed to perform sync signal acquisitionfrom other directions sufficiently frequently; no UE is allocatedresources frequently at a period of T/n where T is the period oftransmitting sync signals by TRPs in the vicinity and n is any positiveinteger; and each UE is informed of the possibility of performing syncsignal acquisition from other directions without losing a communicationopportunity with its serving TRP.

The information about sync signal transmissions from neighboring TRPsmay be acquired by the serving TRP through a backhaul or over the air byoverhearing sync signals from the neighboring TRPs.

Employing Deliberately Large Side-Lobes

In another embodiment, a UE can deliberately employ beam patterns thathave large side-lobes in order to be able to receive signals from otherdirections. The side-lobes can be designed to control the amount ofinterference the UE receives from undesired directions, but still allowsufficiently large signal strength for detection of sync signals.

A UE may choose to employ large-side-lobe beam patterns at all times orat specific time periods it chooses. This can be configured by a TRPserving the UE and/or triggered by the UE itself.

FIG. 13 illustrates a block diagram of an embodiment processing system300 for performing methods described herein, which may be installed in ahost device. As shown, the processing system 300 includes a processor304, a memory 306, and interfaces 310-314, which may (or may not) bearranged as shown in the figure. The processor 304 may be any componentor collection of components adapted to perform computations and/or otherprocessing related tasks, and the memory 306 may be any component orcollection of components adapted to store programming and/orinstructions for execution by the processor 304. In an embodiment, thememory 306 includes a non-transitory computer readable medium. Theinterfaces 310, 312, 314 may be any component or collection ofcomponents that allow the processing system 300 to communicate withother devices/components and/or a user. For example, one or more of theinterfaces 310, 312, 314 may be adapted to communicate data, control, ormanagement messages from the processor 304 to applications installed onthe host device and/or a remote device. As another example, one or moreof the interfaces 310, 312, 314 may be adapted to allow a user or userdevice (e.g., personal computer (PC), etc.) to interact/communicate withthe processing system 300. The processing system 300 may includeadditional components not depicted in the figure, such as long termstorage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system 300 is included in a networkdevice that is accessing, or part otherwise of, a telecommunicationnetwork. In one example, the processing system 300 is in a network-sidedevice in a wireless or wireline telecommunication network, such as abase station, a relay station, a scheduler, a controller, a gateway, arouter, an applications server, or any other device in thetelecommunication network. In other embodiments, the processing system300 is in a user-side device accessing a wireless or wirelinetelecommunication network, such as a mobile station, a user equipment(UE), a personal computer (PC), a tablet, a wearable communicationdevice (e.g., a smartwatch, etc.), or any other device adapted to accessa telecommunication network.

In some embodiments, one or more of the interfaces 310, 312, 314connects the processing system 300 to a transceiver adapted to transmitand receive signaling over the telecommunication network.

FIG. 14 illustrates a block diagram of a transceiver 400 adapted totransmit and receive signaling over a telecommunication network. Thetransceiver 400 may be installed in a host device. As shown, thetransceiver 400 comprises a network-side interface 402, a coupler 404, atransmitter 406, a receiver 408, a signal processor 410, and adevice-side interface 412. The network-side interface 402 may includeany component or collection of components adapted to transmit or receivesignaling over a wireless or wireline telecommunication network. Thecoupler 404 may include any component or collection of componentsadapted to facilitate bi-directional communication over the network-sideinterface 402. The transmitter 406 may include any component orcollection of components (e.g., up-converter, power amplifier, etc.)adapted to convert a baseband signal into a modulated carrier signalsuitable for transmission over the network-side interface 402. Thereceiver 408 may include any component or collection of components(e.g., down-converter, low noise amplifier, etc.) adapted to convert acarrier signal received over the network-side interface 402 into abaseband signal. The signal processor 410 may include any component orcollection of components adapted to convert a baseband signal into adata signal suitable for communication over the device-side interface(s)412, or vice-versa. The device-side interface(s) 412 may include anycomponent or collection of components adapted to communicatedata-signals between the signal processor 410 and components within thehost device (e.g., the processing system 300, local area network (LAN)ports, etc.).

The transceiver 400 may transmit and receive signaling over any type ofcommunication medium. In some embodiments, the transceiver 400 transmitsand receives signaling over a wireless medium. For example, thetransceiver 400 may be a wireless transceiver adapted to communicate inaccordance with a wireless telecommunication protocol, such as acellular protocol (e.g., long-term evolution (LTE), etc.), a wirelesslocal area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any othertype of wireless protocol (e.g., Bluetooth, near field communication(NFC), etc.). In such embodiments, the network-side interface 402comprises one or more antenna/radiating elements. For example, thenetwork-side interface 402 may include a single antenna, multipleseparate antennas, or a multi-antenna array configured for multi-layercommunication, e.g., single input multiple output (SIMO), multiple inputsingle output (MISO), multiple input multiple output (MIMO), etc. Inother embodiments, the transceiver 400 transmits and receives signalingover a wireline medium, e.g., twisted-pair cable, coaxial cable, opticalfiber, etc. Specific processing systems and/or transceivers may utilizeall of the components shown, or only a subset of the components, andlevels of integration may vary from device to device.

It should be appreciated that one or more steps of the embodimentmethods provided herein may be performed by corresponding units ormodules. For example, a signal may be transmitted by a transmitting unitor a transmitting module. A signal may be received by a receiving unitor a receiving module. A signal may be processed by a processing unit ora processing module. Other steps may be performed by a processingunit/module, a storage unit/module, a synchronization unit/module, etc.The respective units/modules may be hardware, software, or a combinationthereof. For instance, one or more of the units/modules may be anintegrated circuit, such as field programmable gate arrays (FPGAs) orapplication-specific integrated circuits (ASICs).

The following embodiments and aspects of the disclosure and can becombined in a possible combination and permutation.

In a first embodiment a method for wireless communication is disclosed.The method comprises transmitting, by a network controller, referencesignals (RS) for beam management to a user equipment (UE), receiving, bythe network controller, a plurality of reported beams from the UE andsignaling, by the network controller, scheduling instructions to the UEbased on the received beams so that the UE is configured to search forsynchronization signals with at least one first beam using a firstantenna set while still being able to receive bearer data with at leastone second beam using a second antenna set during a first time periodfor synchronization, wherein the first antenna set and the secondantenna set are non-overlapping.

According to a first aspect of the disclosure the RS for beam managementcomprises RS for channel state information (CSI) acquisition.

According to a second aspect of the disclosure, the first antenna settransmits a first number of data layers and the second antenna settransmits a second number of data layers, wherein the first and secondnumbers of data layers are equal or smaller than the first and secondantenna sets, respectively.

According to a third aspect of the disclosure, receiving the schedulinginstructions comprises receiving the scheduling instructions so that theUE is configured to receive bearer data via at least one third beam andat least one fourth beam during a second time period, wherein the secondtime period is a time period where the UE does not search for asynchronization signal.

According to a fourth aspect of the disclosure, the at least one thirdbeam is the same as the at least one first beam, and the at least onefourth beam is the same as the at least one second beam.

According to a fifth aspect of the disclosure, the at least one thirdbeam and the at least one fourth beam are different than the at leastone first beam.

According to a sixth aspect of the disclosure, the at least one thirdbeam is the same as the at least one first beam, and the at least onesecond beam is different than the at least one fourth beam.

According to a seventh aspect of the disclosure, the first time periodis larger than T+τ, where T denotes a periodicity of a transmission ofsynchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.

According to a eight aspect of the disclosure, the first time period isequal to T+τ, where T denotes a periodicity of a transmission ofsynchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.

According to a ninth aspect of the disclosure, the plurality of reportedbeams comprises CSIs for beams for a full-layer communication and CSIsfor beams for a reduced-layer communication interval.

According to a tenth aspect of the disclosure, the network controllersignals a different beam for full-layer communication to the UE than forreduced layer communication.

According to an eleventh aspect of the disclosure, the plurality ofreported beams comprises beams associated with a first communicationclass and beams associated with a second communication class.

According to a twelfth aspect of the disclosure, the plurality ofreported beams comprises separate CSIs for beams associated with a firstcommunication class and beams associated with a second communicationclass.

In a second embodiment a method for wireless communication is disclosed.The method comprises receiving, by a user equipment (UE), referencesignals (RS) for beam management from a network controller, reporting,by the UE, a plurality of beams to the network controller and receiving,by the UE, scheduling instructions from the network controller based onthe sent beams so that the UE is configured to search forsynchronization signals with at least one first beam using a firstantenna set while still being able to receive bearer data with at leastone second beam and using a second antenna set during a first timeperiod for synchronization, wherein the first antenna set and the secondantenna set are non-overlapping.

According to a first aspect of the disclosure, the RS for beammanagement comprises a RS for channel state information (CSI)acquisition.

According to a second aspect of the disclosure, the first antenna settransmits a first number of data layers and the second antenna settransmits a second number of data layers, wherein the first and secondnumbers of data layers are equal or smaller than the first and secondantenna sets, respectively.

According to a third aspect of the disclosure, receiving the schedulinginstructions comprises receiving the scheduling instructions so that theUE is configured to receive bearer data via at least one third beam andat least one fourth beam during a second time period, wherein the secondtime period is a time period where the UE does not search for asynchronization signal.

According to a fourth aspect of the disclosure, the at least one thirdbeam is the same as the at least one first beam and the at least onefourth beam is the same as the at least one second beam.

According to a fifth aspect of the disclosure, the at least one thirdbeam and the at least one fourth beam are different than the at leastone first beam.

According to a sixth aspect of the disclosure, the at least one thirdbeam is the same as the at least one first beam and the at least onefourth beam is a beam or set of beams different than the at least onesecond beam.

According to the seventh aspect of the disclosure, the first time periodis larger than T+τ, where T denotes a periodicity of a transmission ofsynchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.

According to the eighth aspect of the disclosure, the first time periodis equal to T+τ, where T denotes a periodicity of a transmission ofsynchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.

According to the ninth aspect of the disclosure, the plurality ofreported beams comprises separate CSIs for beams for a full-layercommunication from and beams for a reduced-layer communication interval.

According to the tenth aspect of the disclosure, the UE receives adifferent beam allocation for full-layer communication from the networkcontroller than for reduced layer communication.

According to an eleventh aspect of the disclosure, the plurality ofreported beams comprises beams associated with a first communicationclass and beams associated with a second communication class.

According to a twelfth aspect of the disclosure, the plurality ofreported beams comprises separate CSIs for beams associated with a firstcommunication class and beams associated with a second communicationclass.

In a third embodiment a method for wireless communication is disclosed.The method comprises synchronizing, by a first network controller,transmission of a first synchronization signal with transmission of asecond synchronization signal from another network controller.

In a fourth embodiment a non-transitory memory storage is disclosed. Thememory storage comprises instructions and one or more processors incommunication with the memory. The one or more processors execute theinstructions for synchronizing transmission of a first sync signal withtransmission of a second sync signal by another TRP.

In a fifth embodiment a network controller is disclosed. The networkcontroller comprises a processor and a non-transitory computer readablestorage medium storing programming for execution by the processor, theprocessor executes instructions for transmitting reference signals (RS)for beam management to a user equipment (UE), receiving a plurality ofreported beams from the UE and signaling scheduling instructions to theUE based on the received beams so that the UE is configured to searchfor synchronization signals with at least one first beam using a firstantenna set while still being able to receive bearer data with at leastone second beam using a second antenna set during a first time periodfor synchronization, wherein the first antenna set and the secondantenna set are non-overlapping.

In a sixth embodiment a user equipment (UE) is disclosed. The UEcomprises a processor and a non-transitory computer readable storagemedium storing programming for execution by the processor, the processorexecutes instructions for receiving reference signals (RS) for beammanagement from a network controller, reporting a plurality of beams tothe network controller and receiving scheduling instructions from thenetwork controller based on the sent beams so that the UE is configuredto search for synchronization signals with at least one first beam usinga first antenna set while still being able to receive bearer data withat least one second beam and using a second antenna set during a firsttime period for synchronization, wherein the first antenna set and thesecond antenna set are non-overlapping.

While this disclosure has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of thedisclosure, will be apparent to persons skilled in the art uponreference to the description. It is therefore intended that the appendedclaims encompass any such modifications or embodiments.

What is claimed is:
 1. A method for wireless communication, the methodcomprising: transmitting, by a network controller, reference signals(RS) for beam management to a user equipment (UE); receiving, by thenetwork controller, a plurality of reported beams from the UE; andsignaling, by the network controller, scheduling instructions to the UEbased on the received beams so that the UE is configured to search forsynchronization signals with at least one first beam using a firstantenna set while still being able to receive bearer data with at leastone second beam using a second antenna set during a first time periodfor synchronization, wherein the first antenna set and the secondantenna set are non-overlapping.
 2. The method according to claim 1,wherein the RS for beam management comprises a RS for channel stateinformation (CSI) acquisition.
 3. The method according to claim 1,wherein the first antenna set transmits a first number of data layersand the second antenna set transmits a second number of data layers,wherein the first and second numbers of data layers are equal or smallerthan the first and second antenna sets, respectively.
 4. The methodaccording to claim 1, wherein receiving the scheduling instructionscomprises receiving the scheduling instructions so that the UE isconfigured to receive bearer data via at least one third beam and atleast one fourth beam during a second time period, wherein the secondtime period is a time period where the UE does not search for asynchronization signal.
 5. The method according to claim 4, wherein theat least one third beam is the same as the at least one first beam, andthe at least one fourth beam is the same as the at least one secondbeam.
 6. The method according to claim 4, wherein the at least one thirdbeam and the at least one fourth beam are different than the at leastone first beam.
 7. The method according to claim 4, wherein the at leastone third beam is the same as the at least one first beam, and the atleast one second beam is different than the at least one fourth beam. 8.The method according to claim 1, wherein the first time period is largerthan T+τ, where T denotes a periodicity of a transmission ofsynchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.
 9. The method according to claim 1, wherein the first timeperiod is equal to T+τ, where T denotes a periodicity of a transmissionof synchronization signals of the network controller and τ denotes aduration of a transmission of synchronization signals of the networkcontroller.
 10. The method according to claim 1, wherein the pluralityof reported beams comprises CSIs for beams for a full-layercommunication and CSIs for beams for a reduced-layer communicationinterval.
 11. The method according to claim 1, wherein the networkcontroller signals a different beam for full-layer communication to theUE than for reduced layer communication.
 12. The method according toclaim 1, wherein the plurality of reported beams comprises beamsassociated with a first communication class and beams associated with asecond communication class.
 13. The method according to claim 1, whereinthe plurality of reported beams comprises separate CSIs for beamsassociated with a first communication class and beams associated with asecond communication class.
 14. A method for wireless communication, themethod comprising: receiving, by a user equipment (UE), referencesignals (RS) for beam management from a network controller; reporting,by the UE, a plurality of beams to the network controller; andreceiving, by the UE, scheduling instructions from the networkcontroller based on the sent beams so that the UE is configured tosearch for synchronization signals with at least one first beam using afirst antenna set while still being able to receive bearer data with atleast one second beam and using a second antenna set during a first timeperiod for synchronization, wherein the first antenna set and the secondantenna set are non-overlapping.
 15. The method according to claim 14,wherein the RS for beam management comprises a RS for channel stateinformation (CSI) acquisition.
 16. The method according to claim 14,wherein the first antenna set transmits a first number of data layersand the second antenna set transmits a second number of data layers,wherein the first and second numbers of data layers are equal or smallerthan the first and second antenna sets, respectively.
 17. The methodaccording to claim 14, wherein receiving the scheduling instructionscomprises receiving the scheduling instructions so that the UE isconfigured to receive bearer data via at least one third beam and atleast one fourth beam during a second time period, wherein the secondtime period is a time period where the UE does not search for asynchronization signal.
 18. The method according to claim 17, whereinthe at least one third beam is the same as the at least one first beamand the at least one fourth beam is the same as the at least one secondbeam.
 19. The method according to claim 17, wherein the at least onethird beam and the at least one fourth beam are different than the atleast one first beam.
 20. The method according to claim 17, wherein theat least one third beam is the same as the at least one first beam andthe at least one fourth beam is a beam or set of beams different thanthe at least one second beam.
 21. The method according to claim 14,wherein the first time period is larger than T+τ, where T denotes aperiodicity of a transmission of synchronization signals of the networkcontroller and τ denotes a duration of a transmission of synchronizationsignals of the network controller.
 22. The method according to claim 14,wherein the first time period is equal to T+τ, where T denotes aperiodicity of a transmission of synchronization signals of the networkcontroller and τ denotes a duration of a transmission of synchronizationsignals of the network controller.
 23. The method according to claim 14,wherein the plurality of reported beams comprises separate CSIs forbeams for a full-layer communication from and beams for a reduced-layercommunication interval.
 24. The method according to claim 14, whereinthe UE receives a different beam allocation for full-layer communicationfrom the network controller than for reduced layer communication. 25.The method according to claim 14, wherein the plurality of reportedbeams comprises beams associated with a first communication class andbeams associated with a second communication class.
 26. The methodaccording to claim 14, wherein the plurality of reported beams comprisesseparate CSIs for beams associated with a first communication class andbeams associated with a second communication class.
 27. A method forwireless communication comprising: synchronizing, by a first networkcontroller, transmission of a first synchronization signal withtransmission of a second synchronization signal from another networkcontroller.